Non-woven fabrics have gained wide acceptance for use in disposable products because of their relatively low cost of manufacture as compared to that of more conventional fabrics made by weaving or knitting processes. They have a wide variety of uses including surgical dressings, incontinence pads, diapers, cigarette filters, quilting or padding, cleaning materials and the like. Such non-woven fabrics are commonly available commercially in a wide range of fabric weights from as little as about ten grams per square meter to as much as about 200 or more grams per square meter.
These items require greater or less dry- and wet-strength according to the use for which they are designed. Extremely low strength materials such as those used for facial cleansing tissues often are required to have substantially no wet-strength. Other items such as bandages should have relatively high dry- and wet-strength to permit use over a period of time in the presence of body fluids or water.
The disposal of these non-woven products, particularly those employed for sanitary purposes and involving containment of body wastes, often has been a problem. Disposal of these items into sewage systems through the restrictive passages of sanitary plumbing may cause clogging. Incineration of such items, particularly where frequent use is necessary and therefore accumulation of considerable amount of disposable material occurs, as in the use of disposable diapers, may also be unsatisfactory.
Various non-woven fabrics have been designed for use in sanitary absorbent products such as diapers and the like which are designed to disintegrate or disperse when the product is placed in water, as in the household toilet. In an effort to provide non-woven fabrics which retain their integrity in the presence of more than limited quantities of aqueous fluids, yet allowing for dispersal of the fibers of the web when this is placed in water, a number of bonding methods have been proposed. Intermittent or random patterns of adhesive or binder resin to bind fibers is disclosed in U.S. Pat. Nos. 2.039,312 and 3,616,797, and other patents; use of stitching is disclosed in U.S. Pat. NO. 2,010,433; use of water-soluble binders in U.S. Pat. Nos. 2,999,038; 3,310,454; 3,370,590; 3,546,716 and 3,554,788 and possibly others; and the use of water-soluble fibers as such is disclosed in e.g. U.S. Pat. Nos. 3,347,236 and 3,550,592. In U.S. Pat. No. 3,480,016 there is described an absorbent product which is water-disperible when an acid or alkali is added to the water, in which a random web of non-woven fibers is bound by means of an acid or alkali sensitive binder.
The water-dispersible product of the prior art, as disclosed in the above-mentioned patents, are not entirely satisfactory for the purposes designed. Some of them are inherently disintegratable in the presence of water, thus maintaining their integrity only in the presence of limited quantities of aqueous fluids. The non-woven products of U.S. Pat. No. 3,480,016, although seemingly stable in water alone, are apparently to a degree unstable in acidic or basic aqueous systems which have pH in the range of that of physiological (body) fluids. In any case it appears that it requires use of added acid or base to disposal systems for effective dispersal of these webs.
While the use of acid- or base-sensitive binders for non-woven webs, which permits disposal after disintegration by means of an acidic or basic reagent, appears to present the best solution thus far advanced for the problem of disposable absorbent materials, this approach is still not believed to be practical. The repeated use of acids or alkalis, whether dilute or concentrated, is believed to be detrimental in the long run to sewage disposal systems depending upon natural organisms for degradation and disposal of sewage. Further, if large numbers of people were to employ such materials in conjunction with municipal disposal systems involving a large central treating station, it is believed that problems would arise in connection with accumulation of acidic or basic materials at some point in the system. Moreover, there is personal hazard inherent in such processes, in the handling, storage and use of the irritating or hazardous chemical reagents required to bring about disintegration of the binders in the aqueous solutions.